1. Field of the Invention
The present invention relates to an image processing apparatus for executing a predetermined process on an input image and for outputting the processed image.
2. Related Background Art
Hitherto, there has existed an apparatus for executing image processes such that a spatial frequency filtering process is digitally executed on input image data, spatial frequency characteristics are changed and the processed data is output. As such an apparatus, a technique in which an input image is separated into three kinds of original character original, screen (or dot) original, and photograph original, and different respective processes are executed them, has been shown in U.S. Pat. No. 4,194,221. On the other hand, a technique in which an edge emphasis process and smoothing filtering process are switched in accordance with an original has been proposed in U.S. Pat. No. 4,953,114, assigned to the same assignee as is the present invention.
However, according to the above conventional technique, for instance, in the case where the kind of input image has been erroneously discriminated, there is a fear that a character of an output image may become extremely dull, the moire of any screen used may be emphasized, or the like, so that the picture quality is remarkably deteriorated. On the other hand, there is a case where, in a portion where the kind of image changes, the picture quality suddenly changes, so that the output image cannot be seen well.
Generally, in a color image copying apparatus, color separation signals of R (red), G (green), and B (blue) are input from an image input device and are subjected to processing such as luminance (light amount)--density conversion, masking, and the like, and a processed image is printed and recorded by an image output device by an ink jet method or an electrophotographic method. In the masking process, color signals of Y (yellow), M (magenta), C (cyan), and K (black) are obtained by matrix calculations from density signals D.sub.r, D.sub.g, and D.sub.b after the density conversion. However, ordinarily, the optimization of masking coefficients a.sub.ij, that is, the non-linear masking, is executed by a method of least squares or the like so as to minimize the color differences within a color reproduction range by using high-order terms such as D.sub.r D.sub.g, D.sub.g D.sub.b, D.sub.b D.sub.r, D.sub.r.sup.2, D.sub.g.sup.2, D.sub.b.sup.2, and the like as well as D.sub.r, D.sub.g, and D.sub.b in consideration of the non-linearity or the like of the image reproducing characteristics of the printer. ##EQU1##
On the other hand, since the discriminating capability of human beings for achromatic color, flesh tints, or the like is high, an advanced color reproducibility is required for a copy image with regard to an original including such colors.
However, according to the above conventional technique, in order to raise the reproducibility of the achromatic color, flesh tints, or the like and to realize a sufficient color reproducibility in the whole color reproduction range, the masking process including the terms of higher order must be executed. Thus, there are drawbacks in that such that the masking circuit becomes complicated and determining the optimum coefficients becomes troublesome.
On the other hand, there are circumstances such that there are individual differences in the degree when color such as achromatic color, flesh tints, or the like .perspectiveto. are perceived by the visual sense of human beings and such degree is dominated by vague parameters based on subjectivity to a certain extent.